“…Based on NP-complete Knapsack cipher, the declared key encryption can be described in three methods, for the first and second method Use them not for authentication but for secrecy, whereas third method was used for authentication but not for secrecy, Shamir [3] studied the feasibility of construction, Merkle and Hellman (1978) propose a public-key system using Knapsack problem [4] by given A={a1,a2,….,an} positive integer and find the positive integer C (cipher text) by C=A.M or C= ,M={m1,m2,….mn} is represent the plaintext (Message) for example if A={10,8,17,20,15,9,6} and M={1,0,1,1,0,0,0} then C=10+17+20=47 The knapsack algorithm is one of the best algorithms to solve arbitrary instances of size n require O( ) time, in a simple Knapsack (super increasing) it solved in linear time algorithm snap (C,A): ("simple Knapsack algorithm") for i:= n down to 1 do begin if C ai then mi=1 else mi=0 C:=C-ai*mi end; if C=0 then snap:=M else " no solution exists " 2.2.1 Example given A=(1,3,5,10,22) and M=(1,1,0,1,0) then to encipher is : C=A*M=(1+3+10)=14 to decipher is : C= 1422 then m5=0 =14-22*0=14 C=1410 then m4=1 =14-10*1=4 C=45 then m3=0 =4-5*0=4…”